The data from numerous high resolution photon scattering experiments allow an extensive survey of the lowest electric dipole excitations in the $A\simeq 130$–200 mass region. In this mass region one can find spherical as well as transitional and strongly quadrupole deformed nuclei. The measured absolute $E1\mathrm{}$ strengths are typically of the order of several milli Weisskopf units and exhibit in general a smooth variation with mass number.

• Received 12 September 1997

DOI:https://doi.org/10.1103/PhysRevC.57.129